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A119833
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Primes p such that 2*p#-1 is prime.
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2
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2, 3, 5, 7, 17, 19, 37, 71, 79, 113, 857, 863, 16361
(list;
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listen;
history;
text;
internal format)
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OFFSET
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1,1
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LINKS
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Table of n, a(n) for n=1..13.
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EXAMPLE
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2*2 - 1 = 3, 3 prime so a(1)=2;
2*2*3 - 1 = 11, 11 prime so a(2)=3;
2*2*3*5 - 1 = 59, 59 prime so a(3)=5.
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MATHEMATICA
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Module[{nn=900, pr, pl}, pr=Prime[Range[nn]]; pl=FoldList[Times, pr]; Select[ Thread[{pr, pl}], PrimeQ[2*#[[2]]-1]&][[All, 1]]] (* Harvey P. Dale, May 02 2018 *)
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PROG
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(Magma) [p:p in PrimesUpTo(4000)|IsPrime(2*&*PrimesUpTo(p)-1)]; // Marius A. Burtea, Mar 25 2019
(Python)
from sympy import isprime, nextprime
def afind(limit):
p = 2
twoprimorialp = 4
while p <= limit:
if isprime(twoprimorialp - 1):
print(p, end=", ")
p = nextprime(p)
twoprimorialp *= p
afind(1000) # Michael S. Branicky, Jan 08 2022
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CROSSREFS
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Cf. A119834, A119835.
Sequence in context: A059498 A247147 A158085 * A127049 A142885 A108547
Adjacent sequences: A119830 A119831 A119832 * A119834 A119835 A119836
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KEYWORD
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nonn,more
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AUTHOR
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Pierre CAMI, May 25 2006
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EXTENSIONS
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a(13) from Michael S. Branicky, Jan 08 2022
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STATUS
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approved
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